Java Program to Check Happy Number

Mathematics for Programming Numbers (Article) Numbers (Program)

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Given Input:

Enter a number to check if it's a Happy Number: 19

Expected Output:

19 is a Happy Number!

Program:

import java.util.HashSet;
import java.util.Scanner;

public class HappyNumberChecker {

    // Function to calculate the sum of squares of digits
    public static int sumOfSquares(int number) {
        int sum = 0, digit;
        while (number > 0) {
            digit = number % 10; // Extract the last digit
            sum += digit * digit; // Add the square of the digit
            number /= 10; // Remove the last digit
        }
        return sum;
    }

    // Function to check if a number is a Happy Number
    public static boolean isHappyNumber(int number) {
        HashSet<Integer> seenNumbers = new HashSet<>();
        
        while (number != 1 && !seenNumbers.contains(number)) {
            seenNumbers.add(number); // Track visited numbers
            number = sumOfSquares(number); // Update the number
        }
        
        return number == 1; // Return true if it reaches 1
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter a number to check if it's a Happy Number: ");
        int number = scanner.nextInt();

        if (isHappyNumber(number)) {
            System.out.println(number + " is a Happy Number!");
        } else {
            System.out.println(number + " is NOT a Happy Number.");
        }

        scanner.close();
    }
}

Output:

Enter a number to check if it's a Happy Number: 20
20 is NOT a Happy Number.

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